1. Field of the Invention
This invention relates generally to pipeline pigs, and more particularly to a pipeline pig having a body formed of resilient foam material and rear and front resilient seal cups apertured to transmit the propelling fluid pressure to both cups and throughout the foam material of the body to radially expand the cups and increase turbulence in the pipeline in front of the pig.
2. Brief Description of the Prior Art
Pipeline pigs are propelled by fluid pressure through the interior of pipelines to clean sludge, scale, debris, and other materials from the inner surfaces of the pipeline. Pipeline pigs are also used to separate different types of products which may be travelling through the same pipeline.
Conventional cup type pipeline pigs usually have two or more resilient cups mounted on an elongate rigid central shaft or on a hollow, generally cylindrical rigid body. The cups have a peripheral lip which extends radially to engage the interior of the pipeline and transmits a radial component of the propelling fluid pressure to the inner walls of pipeline to effect a tighter fit. Some cup type pigs may also be provided with wire brush members on their periphery for scraping the inner wall of the pipeline. Some cup type pipeline pigs may be provided with a tracking device which is usually mounted externally, and is thus subject to being separated and lost.
Although these cup type pipeline pigs have good sealing qualities, because of their substantially inflexible construction, they are not particularly suited for making short radius turns and will often become stuck or will allow fluid to bypass the pig. It is also possible for a steel shaft pipeline pig to cause sparking, should the shaft contact the inner surface of a steel pipeline. In some instances, the weight of the conventional cup type pipeline pigs causes premature wear or distortion of the cup members which can result in fluid leakage. Cup type pipeline pigs are also limited in the type of and quantity of wire brushes which may be installed
Another problem with conventional cup type pigs is that lip of the rearmost cup performs the primary sealing function and the lips of the cups at the forward end receive less fluid pressure and thus do not seal as well or clean as efficiently, and the drop in efficiency increases as the number of cups increase.
Conventional foam type pipeline pigs usually have a generally cylindrical body formed of polyurethane foam. The foam type pipeline pigs are much lighter in weight and are more flexible than the cup type pipeline pigs. However, their sealing properties are not as good, since most commonly known foam type pipeline pigs do not utilize a resilient lip cup seal. The foam type pigs also have more surface area for the installation of peripheral brushes than cup type pigs. However, foam type pigs with brushes have more fluid bypass problems than foam pigs without brushes, due to the lack of a resilient lip cup seal. Some foam type pipeline pigs may be provided with an interior cavity for containing a tracking device which reduces the possibility of the device from being separated and lost.
There are several patents which disclose various foam type pipeline pigs.
Powers, U.S. Pat. No. 4,016,620 discloses a foam type pipeline cleaning pig having a cylindrical open cell foam core with a flexible impervious jacket made of adhesive material which surrounds the outer wall of the core and is covered by abrasive material such as sand, glass, diamond dust, silicon carbides, etc. The abrasive material may also be of the type that contains sharp steel bristles imbedded in a web backing which is secured to the adhesive jacket.
Knapp, U.S. Pat. No. 4,077,079 discloses a foam type pipeline pig having a cylindrical bullet-shaped body of foamed elastomeric plastic that is wrapped with a spiraled cloth which is joined into the body by the elastomeric material which forms the body. The cloth wrapping contains U-shaped wire staples which extend outwardly to form an abrasive surface for cleaning the pipeline.
Girard, U.S. Pat. No. 4,083,076 discloses a foam type pipeline pig having a cylindrical bullet-shaped body of foamed elastomeric plastic that is bonded onto an elongate central column or shaft which extends longitudinally from each end of the body. The shaft is made of high durometer polyurethane, or other material, which is incompressible in the longitudinal direction but is flexible to forces perpendicular to its longitudinal axis to allow the pig to bass obstructions and negotiate moderate bends.
Knapp, U.S. Pat. No. 4,509,222 discloses a pipeline pig having a generally cylindrical relatively hard body formed of high density polyurethane with a pointed nose and a plurality of radially extending flanges or ribs longitudinally spaced along the circumference of the body and a rear area surrounded by a tapered lip which receives the propellant fluid. The body has a central enclosed cavity filled with a low density polyurethane foam and a small restricted opening extending through the rear wall of the cavity. The internal foam filled cavity is exposed to pipeline pressure through the restricted opening at the rear. The restricted opening materially limits a pressure wave from fluid under pressure from entering the foam filled cavity. In the event of a pressure surge, the pressure wave is slowly propagated through the foam which serves as a shock absorber to prevent blowing out the nose of the pig.
The present invention is distinguished over the prior art in general, and these patents in particular by a pipeline pig having an elongate generally cylindrical bullet-shaped body formed of resilient foamed material having a rear end and a nose portion with a resilient rear seal cup secured to the rear end and a resilient front seal cup secured to its forward end near the nose portion. The resilient seal cups have apertures through their central portions and a circumferential rearward facing peripheral lip configured to engage the inner wall of the pipeline. The propelling fluid pressure is transmitted to the rear cup lip to engage it in sealing relation on the inner wall of the pipeline and passes through the rear cup apertures and is propagated throughout the foam material of the body to radially expand the body and exert a radial force on the front cup lip to radially expand and firmly engage the front cup lip in sealing relation on the inner wall of the pipeline. A portion of the propelling fluid pressure propagated throughout the foam material of the body passes to the exterior of the body to exert a propelling force on the front cup lip downstream from the rear cup lip, and a portion of the propelling fluid pressure propagated throughout the foam material of the body passes through the front cup apertures and is propagated throughout the foam material of the nose portion to the exterior of the nose portion and increases turbulence in the pipeline in front of the pig.